Circuit arrangement with a power input and an operating method for controlling a power input circuit

ABSTRACT

A circuit arrangement with a power input and at least one power supply unit that generates a DC voltage for operating an electronic device including a power input circuit inserted between the power input and the at least one power supply unit that selectively disconnects or rectifies an AC voltage provided via the power input for the at least one power supply unit, wherein the power input circuit has at least one first semiconductor switching element that switches a first electrical load path with a current limiting element from the power input to the at least one power supply unit, and at least one second semiconductor switching element that switches a second electrical load path from the power input to the at least one power supply unit, and a power input filter, wherein the power input filter includes a first filter circuit arranged between the power input and the power input circuit and a second filter circuit arranged between the power input circuit and the at least one power supply unit.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/EP2008/059475, withan international filing date of Jul. 18, 2008 (WO 2010/000339 A1,published Jan. 7, 2010), which is based on German Patent Application No.10 2008 031 536.2, filed Jul. 3, 2008, the subject matter of which isincorporated by reference.

TECHNICAL FIELD

This disclosure relates to a circuit arrangement with a power input andat least one power supply unit for generating a DC voltage for operatingan electronic device. The disclosure further relates to an operatingmethod for driving such a power input circuit that is suitable forintegration into such a circuit arrangement.

BACKGROUND

Circuit arrangements with a power input and at least one power supplyunit for generating a DC voltage for operating an electronic device arewidely known. In particular, an ever larger number of devices incommunications and entertainment electronics require at least one powersupply unit to generate a rectified low voltage in the range of 1-24 Vfrom the ordinary 230 VAC mains voltage. The power supply units that areused in that instance must satisfy different, to some extentcontradictory, requirements.

First, the power supply unit must be electronically switched on and off,i.e., without actuating a mechanical switch. This has the advantage,among others, that it is possible to do without high-voltage resistant,relatively expensive power switches and expensive cabling andelectromagnetic shielding in a device housing. In addition, such adevice can be switched on via a timer or other electronic controller.

Second, the power supply unit and the device connected to it shouldconsume as little power from the power grid as possible in a shut-off orstandby state to avoid unnecessary use of energy. Currently availabledevices generally consume a few watts of power in so-called “stand-by”mode, which leads to unnecessary emissions of greenhouse gases for powergeneration.

Third, efficiency of the power supply unit must be as high as possible,and the noise power fed from it into the mains network must be as low aspossible. For this purpose, the power supply unit must comply withincreasingly strict requirements of regulatory agencies and power gridoperators.

Switched-mode power supply units with upstream network filters andcircuits for correcting the power factor are generally used to supplyrelatively large and rapidly varying loads. A clock frequency or a dutyfactor of a control signal is generally used to control the load. Adisadvantage of such circuits is that they have a relatively high powerloss, particularly in standby mode, an operating mode with a very lowoutput power.

It could therefore be helpful to provide a circuit arrangement thatsatisfies the requirements mentioned above particularly well, inparticular, a circuit arrangement and an operating method forcontrolling a power input circuit whose power consumption from a powergrid in the energy-saving state is minimal are to be described. It couldalso be helpful to provide, in the energy-saving state, an arrangementthat preferably does not consume any electrical energy from the powergrid at all. In addition, the circuit arrangement should, to the extentpossible, contain no mechanical or electromechanical switching elementsand be constructed relatively simply.

SUMMARY

I provide a circuit arrangement with a power input and at least onepower supply unit that generates a DC voltage for operating anelectronic device including a power input circuit inserted between thepower input and the at least one power supply unit that selectivelydisconnects or rectifies an AC voltage provided via the power input forthe at least one power supply unit, wherein the power input circuit hasat least one first semiconductor switching element that switches a firstelectrical load path with a current limiting element from the powerinput to the at least one power supply unit, and at least one secondsemiconductor switching element that switches a second electrical loadpath from the power input to the at least one power supply unit, and apower input filter, wherein the power input filter includes a firstfilter circuit arranged between the power input and the power inputcircuit and a second filter circuit arranged between the power inputcircuit and the at least one power supply unit.

I also provide a circuit arrangement with a power input and at least onepower supply unit that generates a DC voltage for operating anelectronic device, including a power input circuit inserted between thepower input and the at least one power supply unit that selectivelydisconnects or rectifies an AC voltage provided via the power input forthe at least one power supply unit, wherein the power input circuit hasat least one first semiconductor switching element that switches a firstelectrical load path with a current limiting element from the powerinput to the at least one power supply unit, and at least one secondsemiconductor switching element that switches a second electrical loadpath from the power input to the at least one power supply unit, and adrive circuit that drives the at least one first semiconductor switchingelement and the at least one second semiconductor switching element,wherein the drive circuit opens the first semiconductor switchingelement and the second semiconductor switching element in anenergy-saving state, closes at least the second semiconductor switchingelement at least temporarily in an operating state, and closes only thefirst semiconductor switching element in a transitional phase from theenergy-saving state to the operating state, the second semiconductorswitching element remaining open.

I further provide an operating method for driving a power input circuitwith at least one first semiconductor switching element for switching afirst electrical load path with a current-limiting element from a powerinput to at least one power supply unit and at least one secondsemiconductor switching element for switching a second electrical loadpath from the power input and to the power supply unit, includingopening the first and the second semiconductor switching element in anenergy-saving state, at least temporarily closing the firstsemiconductor switching element and leaving the at least one secondsemiconductor switching element open in a transition phase from theenergy-saving state to an operating state, and at least temporarilyclosing the at least one second semiconductor switching element in theoperating state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a circuit arrangement with apower input circuit.

FIG. 2 shows a conventional power input circuit.

FIG. 3 shows a power input circuit according to a first example.

FIG. 4 shows a state diagram of an operating method for controlling apower input circuit.

FIG. 5 shows a power input circuit according to a second example.

DETAILED DESCRIPTION

We provide a circuit arrangement of this generic type that may have apower input circuit inserted between the power input and the at leastone power supply unit for selective disconnection or rectification of anAC voltage provided for the at least one power supply unit via the powerinput. The power input circuit has at least one first semiconductorswitching element for switching at least one first electrical load pathwith a current limiting element from the power input to the at least onepower supply unit, and at least one second semiconductor switchingelement for switching at least one second electrical load path from thepower input to the at least one power supply unit.

Due to the fact that the power input circuit can selectively disconnectthe at least one power supply unit from the grid voltage, power loss inthe energy-saving state of the at least one power supply unit can beavoided. By selectively rectifying the provided AC voltage by means ofthe power input circuit, it is possible to forgo the use of anadditional rectifier in or upstream of the at least one power supplyunit.

A load current for the at least one power supply unit alternativelyflows in a first electrical load path with a current-limiting element,or in a second electrical load path from the power input to the powersupply unit. Due to the use of a current-limiting element in the firstload path, an overload of the provided AC voltage by the power supplyunit during switching-on can be prevented. By switching the secondelectrical load path, a power loss due to the current-limiting elementin normal operation of the power supply unit can be prevented.

The at least one semiconductor switching element and/or the secondsemiconductor switching element may be a thyristor. The use of athyristor allows a selective disconnection or rectification of aprovided AC voltage by a relatively simple circuit construction.

The power input circuit may have at least one rectifier circuit with asemiconductor bridge rectifier, and the at least one secondsemiconductor switching element forms a part of the semiconductor bridgerectifier. By combining the functions of selective disconnection orrectification in the second semiconductor switching element, the powerloss of the power input circuit is reduced.

The circuit arrangement may be characterized by a power input filter,wherein the power input filter comprises a first filter circuit arrangedbetween the power input and the power input circuit and a second filtercircuit arranged between the power input circuit and the at least onepower supply unit. By dividing the power input filter into a firstfilter circuit arranged on the input or grid side and a second filtercircuit arranged on the output or power supply unit side, reactive orlost power of the circuit arrangement in an energy-saving state can befurther reduced.

The circuit arrangement circuit may be characterized by an overvoltagefilter, the overvoltage filter being arranged between the power inputcircuit and the at least one power supply unit. By arranging theovervoltage filter downstream of the power input circuit, it uses noelectrical energy in the energy-saving state.

The circuit arrangement may be characterized by a drive circuit fordriving the at least one first semiconductor switching element and theat least one second semiconductor switching element, wherein the drivecircuit is set up to open the first semiconductor switching element andthe second semiconductor switching element in an energy-saving state andto close the second semiconductor switching element, to temporarilyclose the at least one second semiconductor switching element in anoperating state, and to close only the first semiconductor switchingelement at least temporarily in a transition phase from theenergy-saving state to the operating state, wherein the secondsemiconductor switching element remains open.

Power consumption of the circuit arrangement in the energy-saving statecan be completely or almost completely avoided by opening or switchingoff the semiconductor switching elements in the energy-saving state. Byclosing or switching on only the first semiconductor switching elementin a transition phase and leaving the second semiconductor switchingelement open, a current surge when the circuit arrangement is switchedinto the operating state is limited by the current-limiting element. Byclosing the second switching element in an operating state, the creationof an undesired power loss at the current-limiting element is avoided.

The circuit arrangement may be set up to supply the drive circuit in theenergy-saving state and/or the transition phase with an energy storagedevice preferably arranged in the electronic device. By supplying thedrive circuit from an energy-storage device in the transition phaseand/or the energy-saving state, drawing electric power from the powerinput in these states can be forgone.

The circuit arrangement may be set up to supply the drive circuit withenergy in the operating state by means of the at least one power supplyunit. By supplying the drive circuit in the operating state with the atleast one power supply unit, the load on the energy storage device canbe reduced.

The drive circuit may comprise at least one third semiconductorswitching element, by which a first drive circuit for driving the atleast one first semiconductor switching element and a second drivecircuit for driving the at least one second semiconductor switchingelement can be coupled to one another. By selective coupling of a firstdrive circuit and second drive circuit, circuitry for driving the firstand second semiconductor elements can be simplified.

An operating method may be provided for driving a power input circuitwith at least one first semiconductor switching element for switching afirst electrical load path with a current-limiting element from a powerinput to at least one power supply unit and at least one secondsemiconductor switching element for switching a second electrical loadpath from the power input to the power supply unit. The operating methodcomprises:

-   -   opening the first and second semiconductor switching elements in        an energy-saving state;    -   at least temporarily closing the first semiconductor switching        element and leaving the at least one second semiconductor        switching element open in a transition phase from the        energy-saving state to an operating state; and    -   at least temporarily closing the at least one second        semiconductor switching element in the operating state.

By such an operating method, an electrical connection between the firstpower input and the power supply unit is initially interrupted in anenergy-saving state to prevent or minimize power consumption. In anadditional step, the first semiconductor switching element is closed toprovide an initial operating current via the at least one electricalload path to the power supply unit, wherein the current-limiting elementlimits an increase of the power consumption. Finally a power loss in theoperating state caused by the current-limiting element is avoided byclosing the second semiconductor switching element.

Additional advantageous configurations are disclosed in the descriptionbelow. My methods and apparatus will be explained in detail withreference to the examples and the figures below.

FIG. 1 shows a schematic representation of a circuit arrangement 1 forsupplying an electronic device with an operating voltage. The circuitarrangement 1 in accordance with FIG. 1 comprises a power input 2, apower input circuit 4, and a first and second power supply unit 3A and3B.

The power input 2 is used for coupling the circuit arrangement 1 to anAC voltage of a power supply network, for example, an AC network with avoltage of 230 V. The power input circuit 4 is used to prepare andfilter the AC voltage received by the power input 2 for the downstreampower supply units 3A and 3B.

An arrangement with two power supply units 3A and 3B is shown in FIG. 1.For example, the first power supply unit is an auxiliary power supplyunit 3A for supplying the electronic device in an operating mode withreduced power consumption, and the normal power supply unit 3B is a mainpower supply unit for normal operation of the electronic device. Thefirst power supply unit 3A is optionally connected to the second powersupply unit 3B, for example, to enable a starting process for startingthe second power supply unit 3B by the first power supply unit 3A.

The use of two differently dimensioned power supply units has theadvantage that a relatively high efficiency of the circuit arrangementcan be achieved even in an operating mode with a reduced powerconsumption. Of course, the power input circuit described herein is alsosuitable for those arrangements with only a single power supply unit.

In the schematic representation according to FIG. 1, the power inputcircuit 4 comprises a power input filter 5 and a rectifier circuit 6.The power input filter filters out noise from the power grid and/ornoise caused by the power supply units 3A and 3B. Particularly forswitched-mode power supplies, relatively large, high-frequency currentsdue to the switching appear at the power supply units 3A and 3B, whichcan lead to a malfunction of the power supply network. Therefore thepower input filter 5 comprises a low-pass filter, for example.

Before turning to the various examples for solving the fundamentalproblem, a conventional circuit arrangement will first be explained.

FIG. 2 shows a circuit arrangement 1′ according to the prior art. Thecircuit arrangement 1′ comprises a power input 2 in the form of a phaseinput LINE and a neutral conductor NEUTRAL, which are coupled via apower input filter 5 to a rectifier circuit 6 in the form of a bridgerectifier BDI. The power input filter 5 comprises x-capacitors Cx1 andCx2 arranged between the phase input LINE and neutral conductor NEUTRAL,y-capacitors Cy1, Cy2, Cy3, Cy4 arranged between the neural conductorNEUTRAL and electrical ground, suppression inductors L1 and L2 arrangedrespectively in the phase line LINE and the neutral conductor NEUTRAL,and a resistor Rdis inserted between the phase line LINE and the neutralconductor NEUTRAL. The bridge rectifier BDI comprises four diodes thatare arranged in a so-called “Graetz bridge” and convert an AC voltage atthe terminals AC1 and AC2 into a pulsating DC voltage at the terminals +and −. The actual power supply unit is not shown in FIG. 2. In thecircuit arrangement 1′ of FIG. 2 it was connected in parallel to thestorage capacitor labeled C1.

To avoid a large charging current in the phase line LINE when the powersupply unit is switched on by the switch Sw, a current-limiting elementin the form of an NTC resistor Rntc is inserted between the rectifierBDI and the storage capacitor C1. The NTC resistor limits the chargecurrent of the capacitor C1 when it is turned on. To avoid the parasiticload of the NTC resistor Rntc in the operation of the circuitarrangement 1, a monostable relay REL is provided. The current-limitingelement Rntc can be bridged by applying a voltage of, for example,twelve volts between the control terminals A and B of the relay REL.

One disadvantage of the circuit arrangement 1′ shown in FIG. 2 is thatthe relay REL must always be supplied with a supply voltage in theoperating state to bridge the current-limiting element. Anotherdisadvantage is that the power input filter 5 and the storage capacitorC1 are always connected to the power supply network when the switch Swis closed. Even if a power supply unit were to draw no charge from thestorage capacitor C1, the power input filter 5 would lead to reactiveand lost power by the circuit arrangement 1. The discharge resistor Rdisof the power input filter 5 also contributes to the power loss of thecircuit arrangement 1′ in a switched off or energy-saving state of thepower supply unit 3. This is necessary for safety reasons to dischargethe x-capacitors Cx1 to Cx2, which can have a capacitance of more than100 nF, in a controlled manner when the power supply is switched off.Finally, the switch Sw must be designed to be resistant to currentsurges to guarantee a safe and repeated switching on and off of thecircuit arrangement 1′.

FIG. 3 shows one example of a circuit arrangement 1. The circuitarrangement 1 again comprises a power input 2 with a phase line LINE anda neutral conductor NEUTRAL. In addition, the power input 2 has two verysmall-dimensioned filter elements L1 and L1′. For example, the lattercan be annular ferrite elements, through which a power input line of thecircuit arrangement 1 is run. The circuit arrangement 1 furthercomprises a power input circuit 4 comprising four diodes BR1-BR4 as wellas three thyristors SCR1-SCR3. The power input circuit 4 furthercomprises a current-limiting element in the form of an NTC resistorRntc, as well as a switch Sw1 for bridging the thyristor SCR1. Theswitch Sw1 is used for short-time switching over between theenergy-saving state without power consumption and a conventional standbystate, in which power is drawn from the power supply network. Thisbridging can be used, for example, to charge the storage capacitor C1and thus allow the start-up of a power supply unit 3 even if anactivation of the thyristor SCR1 is no longer possible on the secondaryside, for example, because a battery cell provided for this purpose wascompletely discharged.

An overvoltage filter 7 in the form of a voltage-dependent resistor VDRis arranged at the output of the power input circuit 4. The resistor VDRis not necessary for the functioning of the circuit arrangement 1,however. Finally, the circuit arrangement 1 comprises a power inputfilter 5 that is arranged between the power input circuit 4 and astorage capacitor C1. A power supply unit 3 not shown in FIG. 3 isconnected in parallel to the storage capacitor C1.

The power input circuit 4 is driven by two transformers T1 and T2. Thedrive circuit required for this is not shown in FIG. 3, however.

The operation of the circuit according to FIG. 3 will be explained indetail using the state diagram in accordance with FIG. 4.

In a switched-off or energy-saving state Z0, the thyristors SCR1-SCR3block. Thus, there is no electrically conductive path from the powerinput LINE to the neutral conductor NEUTRAL, so that no current flows inFIG. 3 and neither lost power nor reactive power appears.

By applying a signal sequence of pulses to the transmitter T1, a pulsetrain is transmitted to the control terminal of the thyristor SCR1.Since no zero crossing recognition is performed in the circuit accordingto FIG. 3, a permanent DC voltage can be applied according to a firstconfiguration as a control signal to the thyristor SCR1. For thefunctioning of the circuit, it is sufficient at a frequency of 50 Hz,however, to generate a drive pulse roughly every 2 ms, so that thethyristor is triggered approximately 10 times per power supply waveperiod. This causes the thyristor SCR1 to become conductive in onedirection and thus act as a semiconductor switching element. This isshown as a step 31 in FIG. 4.

If there is a positive half wave on the phase line LINE, the currentflows in the circuit according to FIG. 3 from the phase input LINE viathe filter element L1, the diode BR3, the current limiting element Rntc,and the thyristor SCR1 to the power input filter 5 and the storagecapacitor C1. The return flow from the power input filter 5 and thestorage capacitor C1 to the neutral conductor NEUTRAL takes place viathe diode BR2 and the filter element L1′. In the opposite case, i.e.,with a negative half wave at the phase input LINE, a current flows fromthe neutral conductor NEUTRAL via the filter element L1′, the diode BR1,the NTC resistor Rntc, and the thyristor SCR1 to the power input filter5 and the storage capacitor C1, and from there back to the phase inputLINE via the diode BR4 and the filter element L1.

By connecting the phase line LINE and the neutral conductor NEUTRAL viathe diodes BR1, BR2, BR 3, and BR4, the thyristor SCR1 can therefore beused in both pathways for activating or deactivating the circuitarrangement 1. Thus only a single switching element in the circuitarrangement 1 is necessary to charge the storage capacitor C1.

If the storage capacitor C1 has been charged and the connected powersupply unit 3 has begun operation, the thyristors SCR2 and SCR3 are alsodriven in an additional step 32 a. According to FIG. 3, a second controlsignal is applied to the second transformer T2 for this purpose. Theoutput of the second transformer T2 is connected to both thyristors SCR2and SCR3, so that they are driven jointly in the illustrated exemplaryembodiment. Optionally, the thyristor SCR1 can be opened simultaneouslyor later in a step 32 b, for example, by not transmitting any additionalcontrol signals to the first transformer T1. Is not essential to thefunctioning and the efficiency of the circuit arrangement 1 because thecurrent always chooses the path of least electrical resistance when thethyristors SCR2 and SCR3 are triggered.

The thyristors SCR2 and SCR3 are advantageously driven with a higherfrequency than the driving of the thyristor SCR1, for example, afrequency of 1 kHz. Depending on the phase position of the power supplyvoltage and the quality of the power input filter, relatively largecurrent surges and/or the generation of whistling noises can take placehowever. To avoid this, it is advisable to use a drive frequency ofroughly 3 kHz or even better, 5 kHz. A higher frequency relative to thefrequency of the power supply network has the advantage that no largecharging interruptions appear after a zero crossing of the supplyvoltage, and therefore a noise level of the circuit arrangement isfurther reduced. For further improvement of the drive circuit, the dutyratio used for driving the transformer T2 can be selected larger thanthe duty ratio of the transformer T1 to compensate for the shorterdriving periods and guarantee a secure triggering of the thyristors SCR2and SCR3.

In a positive half wave on the phase line LINE, a current flows via thefilter element L1 and the thyristor SCR3 to the power input filter 5 andthe storage capacitor C1. From there the current flows back to theneutral conductor NEUTRAL via the diode BR2 and the filter element L1′.In the opposite case, i.e., in case of a negative half wave, the currentflows from the neutral conductor NEUTRAL via the filter element L1′ andthe thyristor SCR2 to the power input filter 5 and the storage capacitorC1. The power flows back from there to the phase input LINE via thediode BR4 and the filter element L1.

In the circuit arrangement according to FIG. 1 with a first power supplyunit 3 a and a second power supply unit 3 b, a multistage switch-onmethod can also be used. After the initial charging of the storagecapacitor C1, it is possible, for example, to start only the first powersupply unit 3 a, a relatively low-power auxiliary power supply unit inthis example, and to use the output current of the first power supplyunit 3 a to drive the thyristors SCR2 and SCR3. Only then is acorresponding control device, such as a microcontroller, started, aswell as the second power supply unit 3 b, a more powerful power supplyunit, for example.

As is further illustrated in FIG. 4, an essentially opposite switchingsequence can be used in switching the circuit arrangement 1 from theoperating state Z1 to the energy-saving state Z0. In a first step 33,the thyristors 33 are opened. If the thyristor SCR1 is still closed atthis time, the current for operating the power supply unit 3 again flowsvia the current-limiting element Rntc. If it is already open, a currentflow is immediately stopped. It is, of course, also possible todeactivate the thyristor SCR1 simultaneously with the thyristors SCR2and SCR3, by deactivating the corresponding drive signals, for example.

Closing the first semiconductor switching element or leaving it closedby, for example, supplying the thyristor SCR1 with a continued drivesignal, has advantages particularly in case of a failure or malfunctionof a supply network connected to the power input 2. If a power networkvoltage is lost only for a short time, a power surge during there-provision of the supply voltage can be avoided via the load pathcharacterized by the current-limiting element Rntc. At the same time,the continuous operation of the power supply unit or units ismaintained, if the malfunction lasts only such a short time that it canbe bridged by the storage capacitor C1.

In another optional step 34, the thyristor SCR1 is also opened or nolonger driven so that the power supply unit 3 and the power filter 5 aredisconnected by the power input circuit 4 from the power supply network.Thus, the circuit arrangement returns to the operating state Z0, inwhich it no longer consumes any electric power.

The circuit arrangement 1 according to FIG. 3 has several advantagescompared to the circuit arrangement 1′ of FIG. 2. First, it is possibleto forgo the use of a relay. By using only semiconductor components fordisconnecting or connecting the power supply unit 3 from the power input2, the operating safety of the circuit arrangement 1 is increased.

Moreover, arranging the thyristors SCR2 and SCR3 in a bridge circuitsimultaneously provides a rectification function. By uniting thefunctions of power supply network disconnection and rectification, theefficiency achieved by the circuit arrangement 1 overall is increased.It is true that a slightly higher voltage drops at the thyristors SCR2and SCR3 than at the diodes of a conventional bridge rectifier, but thisadditional power loss is more than compensated by avoiding an additionalrectifier or a relay for bridging the NTC resistor Rntc.

For example, with a rectifier circuit having one thyristor with avoltage drop of 1.0 V and one diode with a voltage drop of 0.8 V perphase, a voltage drop of 1.8 V occurs. For a rectifier circuit with twodiodes per phase, on the other hand, a voltage drop of only 1.6 Voccurs. For an average load current of 0.5 A, the additional voltagedrop of 0.2 V corresponds to extra expenditure of 0.1 W in operation.This extra expenditure is countered by the savings from not driving anadditional relay in operation and the additional energy savings in theenergy-saving state, so that an overall positive energy balance results.

Furthermore, the circuit arrangement 1 according to FIG. 3 has nosuppression capacitors on the primary side, i.e., between the powerinput 2 and the power input circuit 4. The resistor Rdis necessary fordischarging the storage capacitor C1 is likewise disconnected from thepower input 2 by the power input circuit 4. Therefore, no loss orreactive power occurs at the power input 2 with the thyristors SCR1-SCR3open.

Finally, there is no significantly increased requirement for componentsin comparison to conventional circuit arrangements for supplying power.The circuit arrangement does require the semiconductor switchingelements SCR1-SCR3, but mechanical relays or switches are no longernecessary. In addition, the thyristors SCR2 and SCR3 used as switchingelements partially replace the rectifier diodes used in conventionalcircuits.

FIG. 5 shows an additional example of a circuit arrangement 1. Thecircuit arrangement 1 according to FIG. 5 comprises a first filtercircuit 5A arranged between a power input 2 and a power input circuit 4.The circuit arrangement 1 further comprises an overvoltage filter 7 aswell as a second filter circuit 5B which are arranged electricallydownstream of the power input circuit. Together the filter circuits 5Aand 5B form a power input filter 5. Downstream of the second power inputfilter 5B, a circuit for active power factor correction PFC is arranged.The circuit for power factor correction PFC is used to reduce theinterference in the power supply network produced by the switched-modepower supply unit. A storage capacitor and a switched-mode power supplyunit 3, not shown in FIG. 5, are connected downstream of the powerfactor correction circuit PFC.

The power input circuit 4 is very similar to the power input circuit 4shown in FIG. 3. It again comprises three thyristors SCR1-SCR3 as wellas four diodes D1-D4, which together form a disconnectable rectifiercircuit 6. The power input circuit 4 additionally comprises acurrent-limiting element in the form of an NTC resistor Rntc in a firstelectrical load path, and a second electrical load path via thethyristors SCR2 and SCR3 does not have any such current-limiting means.

A switch Sw1 is again provided to start the circuit according to FIG. 5even in the case where a secondary-side driving of the thyristor SCR1 isno longer possible, for example, because an energy storage device of adownstream device is exhausted. Differently from the configurationaccording to FIG. 3, the switch Sw1 does not bridge the thyristor SCR1from its anode to its cathode, but instead provides a trigger voltage toits control terminal or gate via a series resistor R2. For this purpose,the series resistor R2 is connected between the diodes D3 and D4 andtherefore always provides a positive control voltage, independently ofthe phase position at the power input 2. Alternatively the drive voltagecan also be tapped between the NTC resistor Rntc and the first thyristorSCR1. This circuit structure has the advantage that the switch Sw1 neednot be constructed to be resistant to current surges. In particular, acontrol current of only a few milliamperes suffices to trigger thethyristor SCR1.

FIG. 5 additionally shows a drive circuit 8 for driving the thyristorsSCR1-SCR3. Unlike the circuit arrangement in FIG. 3, the drive circuit 8has only a single transformer T0.

The transformer T0 is supplied by a MOSFET transistor Q1 with a pulsesignal by means of a control signal SCR. In the example according toFIG. 5, the transformer T0 is used to drive the first thyristor SCR1with square wave pulses of a first drive frequency, for example, 500 Hz.Alternatively, a variable, more dense train of drive pulses can begenerated to securely guarantee triggering of the thyristor SCR1 in allphase conditions. Such a relatively low-frequency drive signal can begenerated by a secondary voltage source. The battery cell installed inthe circuit arrangement 1 or in an electronic device connected thereto,such as the CMOS battery of a computer or laptop, is suitable for thispurpose.

By applying a square wave pulse to the transformer T0, it is firstre-magnetized. If the excitation voltage drops, the capacitor C3 will becharged via the diode D5 by the magnetization current from T0, andcapacitor C1 will continue to be charged via the diode D6. Then thethyristor SCR1 will be triggered via the series resistor R1. Thereby avoltage results at the capacitor C3 that corresponds to the controlvoltage of the thyristor SCR1, the voltage drop at the resistor R1 andthe additional forward voltage of diode D6, for example, 1.4 to 2 V.

By closing a transistor Q2 of the drive circuit 8, the thyristors SCR2and SCR3 can additionally be driven by the transformer T0. For thispurpose, a control input OPTO of an optocoupler U1 is drawn to groundpotential to generate a control signal for the transistor Q2. Theresistors R35 and R36 are dimensioned such that the transistor Q2 iswell supplied with base current and a voltage drop on thecollector-emitter path of Q2 is low, for example, 0.4 V.

In this manner the pulse signal generated by the transformer T0 is alsoprovided for the thyristors SCR2 and SCR3. As described above, thetransformer T0 is preferably driven for this purpose with a higher clockfrequency, for example 1 kHz, and a higher duty ratio. The diode D6 isused to artificially raise a charge voltage at the capacitor C3 withrespect to the voltage at the capacitor C1 to have a voltage reserve fortriggering the thyristors SCR2 and SCR3 compared to the triggering ofSCR1. In this way it is assured in the normal operating state Z1 thatthe thyristors SCR2 and SCR3 always securely trigger and that no loss ofpower results from bridging the current-limiting element Rntc. At thesame time the thyristor SCR1 is no longer driven, since only a reduceddrive voltage is available at its control terminal.

The circuit arrangement 1 according to FIG. 5 has the advantage that aparticularly good interference suppression of a switched-mode powersupply becomes possible. Nevertheless, only a part of the power inputfilter 5 connects to the power supply network in the energy-saving stateZ0. The first filter circuit 5A has no resistor and no x-capacitors, sothat no real power and only a small amount of reactive power appear init. The elimination of a resistor is enabled by the fact, among others,that x-capacitors are forgone in the first filter circuit 5A, andadditionally that the capacitance of the y-capacitors is on the order of1 nF, so that there is no need for a discharge resistor.

In addition, the drive circuit 8 is constructed particularly simply. Asa matter of course, each semiconductor switching element SCR1-SCR3 mustbe driven separately. But since the thyristors SCR2 and SCR3 onlyconduct in a preferred direction anyway, the two thyristors can bedriven with a common control signal. By optionally coupling drivecircuits for the thyristor SCR1 and for the thyristors SCR2 and SCR3,expense for components and driving is further reduced.

1-15. (canceled)
 16. A circuit arrangement with a power input and atleast one power supply unit that generates a DC voltage for operating anelectronic device comprising a power input circuit inserted between thepower input and the at least one power supply unit that selectivelydisconnects or rectifies an AC voltage provided via the power input forthe at least one power supply unit, wherein the power input circuit hasat least one first semiconductor switching element that switches a firstelectrical load path with a current limiting element from the powerinput to the at least one power supply unit, and at least one secondsemiconductor switching element that switches a second electrical loadpath from the power input to the at least one power supply unit, and apower input filter, wherein the power input filter comprises a firstfilter circuit arranged between the power input and the power inputcircuit and a second filter circuit arranged between the power inputcircuit and the at least one power supply unit.
 17. The circuitarrangement according to claim 16, wherein the at least firstsemiconductor switching element and/or the at least second semiconductorswitching element is a thyristor.
 18. The circuit arrangement accordingto claim 16, wherein the power input circuit comprises at least onerectifier circuit with a semiconductor bridge rectifier and the at leastone second semiconductor switching element forms a part of thesemiconductor bridge rectifier.
 19. The circuit arrangement according toclaim 16, wherein the first filter circuit has no resistor and nox-capacitors.
 20. The circuit arrangement according to claim 16, whereinthe first filter circuit has a capacitance of less than 68 nF.
 21. Thecircuit arrangement according to claim 16, further comprising anovervoltage filter arranged between the power input circuit and the atleast one power supply unit.
 22. The circuit arrangement according toclaim 16, further comprising a drive circuit that drives the at leastone first semiconductor switching element and the at least one secondsemiconductor switching element, wherein the drive circuit opens thefirst semiconductor switching element and the second semiconductorswitching element in an energy-saving state closes at least the secondsemiconductor switching element at least temporarily in an operatingstate, and closes only the first semiconductor switching element atleast temporarily in a transition phase from the energy-saving state tothe operating state, and wherein the second semiconductor switchingelement remains open.
 23. The circuit arrangement according to claim 22,wherein the circuit arrangement supplies the drive circuit in theenergy-saving state and/or the transition phase with an energy storagedevice of the electronic device.
 24. The circuit arrangement accordingto claim 23, wherein the energy storage device is arranged in theelectronic device.
 25. The circuit arrangement according to claim 23,wherein the circuit arrangement supplies the drive circuit with energyin the operating state with at least one power supply unit.
 26. Thecircuit arrangement according to claim 22, wherein the drive circuitcomprises at least one transformer that galvanically separates theelectronic device from the power input circuit.
 27. The circuitarrangement according to claim 22, wherein the drive circuit comprisesat least one third semiconductor switching element, by which a firstdrive circuit that drives the first semiconductor switching element anda second drive circuit that drives the at least one second semiconductorswitching element can be coupled to one another.
 28. The circuitarrangement according to claim 22, wherein the drive circuit generates aclocked control signal with a first, lower frequency in a transitionphase and generates a clocked control signal with a second, higher drivefrequency in the operating state.
 29. A circuit arrangement with a powerinput and at least one power supply unit that generates a DC voltage foroperating an electronic device, comprising: a power input circuitinserted between the power input and the at least one power supply unitthat selectively disconnects or rectifies an AC voltage provided via thepower input for the at least one power supply unit, wherein the powerinput circuit has at least one first semiconductor switching elementthat switches a first electrical load path with a current limitingelement from the power input to the at least one power supply unit, andat least one second semiconductor switching element that switches asecond elegrical load path from the power input to the at least onepower supply unit; and a drive circuit that drives the at least onefirst semiconductor switching element and the at least one secondsemiconductor switching element, wherein the drive circuit opens thefirst semiconductor switching element and the second semiconductorswitching element in an energy-saving state, closes at least the secondsemiconductor switching element at least temporarily in an operatingstate, and closes only the first semiconductor switching element in atransitional phase from the energy-saving state to the operating state,the second semiconductor switching element remaining open.
 30. Thecircuit arrangement according to claim 29, wherein the power inputcircuit comprises at least one rectifier circuit with a semiconductorbridge rectifier, and the at least one second semiconductor switchingelement forms part of the semiconductor bridge rectifier.
 31. Thecircuit arrangement according to claim 29, wherein the first filtercircuit has no x-capacitors.
 32. The circuit arrangement according toclaim 29, wherein the drive circuit generates a clocked control signalwith a first, lower drive frequency in the transition phase, and aclocked signal with a second, higher frequency in the operating phase.33. An operating method for driving a power input circuit with at leastone first semiconductor switching element for switching a firstelectrical load path with a current-limiting element from a power inputto at least one power supply unit and at least one second semiconductorswitching element for switching a second electrical load path from thepower input and to the power supply unit, comprising: opening the firstand the second semiconductor switching element in an energy-savingstate; at least temporarily closing the first semiconductor switchingelement and leaving the at least one second semiconductor switchingelement open in a transition phase from the energy-saving state to anoperating state; and at least temporarily closing the at least onesecond semiconductor switching element in the operating state.
 34. Theoperating method according to claim 33, further comprising at leasttemporarily closing the first semiconductor switching element andopening the at least one second semiconductor switching element in atransition phase from an operating state to the energy-saving state whena malfunction of a supply network connected to the power input has beenrecognized.
 35. The operating method according to claim 33, wherein aclocked control signal with a first, lower drive frequency is generatedin the transition phase, and a clocked control signal with a second,higher drive frequency is generated in the operating state.